1. Field of the Invention
The present invention relates to a multi-layer printed circuit board and a fabricating method thereof, and more particularly, to a multi-layer printed circuit board having copper patterns at an upper surface and a lower surface thereof and having a connection portion for electrically connecting the copper patterns therein, and a fabricating method thereof.
2. Description of the Conventional Art
Generally, a printed circuit board is variously used in electronic devices or electronic goods, and becomes multi-layered and high-densified as the electronic industry is developed. At the time of fabricating the printed circuit board, many processes and precise technique are required.
Copper patterns are formed at an upper surface and a lower surface of the multi-layer printed circuit board, and a connection portion for electrically connecting the copper patterns is formed at the printed circuit board in a vertical direction or a laminated direction.
As one example of the connection portion, a technique for using an anisotropy conductive adhesive was disclosed. According to the anisotropy conductive adhesive formed by dispersing minute conductive particles in an adhesion sheet, when a certain pressure is applied to the conductive adhesive in a vertical direction, the part to which the pressure has been applied selectively shows a conductivity and this characteristic of the anisotropy conductive adhesive was used for the connection portion.
Also, a technique for forming a hole at a printed circuit board and then plating an inner circumferential surface of the hole thereby electrically connecting copper patterns formed at an upper surface and a lower surface of the printed circuit board was disclosed.
According to the Korean patent No. 203, 540 (U.S. Pat. No. 5,600,103), as shown in FIG. 1, conical conductive wiring parts 2′ are positioned in an inter-connector 1 with penetrating a synthetic resin based sheet 4. A lower portion of the conical conductive wiring parts 2′ is electrically connected to copper patterns 3, and an upper portion of the conical conductive wiring parts 2′ is used as a connecting terminal with an exposed state from the surface of the synthetic resin based sheet 4. The conductive wiring parts 2 are formed with a certain height accordingly as a conductive paste is repeatedly printed on the copper pattern 3 by a screen printing method. Then, the synthetic resin based sheet 4 is positioned on the conductive wiring parts 2 and is compressed by a roller, etc., so that the conductive wiring parts 2 are protruded out by penetrating the synthetic resin based sheet 4.
According to the Japanese Laid-Open Publication Patent No. 2001-111189 (U.S. Pat. No. 6,528,874), as shown in FIG. 2A, a base member 10 that an etching resist layer 13 of a nickel material is interposed between a first copper layer 11 and a second copper layer 12 is provided. The first copper layer 11 is to be served as a connection portion 16 in the next process, and is formed to be thicker than the second copper layer 12. The second copper layer 12 is to be served as a copper pattern 19 in the last process.
As shown in FIGS. 2B and 2C, resist layers 14 and 14′ are formed at both surfaces of the base member 10, and a specific part of the resist layer 14′ positioned at the first copper layer 11 where the connection portion 16 is to be formed is removed thereby to form an etching opening 15. A part of the first copper layer 11 exposed through the etching opening 15 is etched thereby to be removed, and the first copper layer 11 that has not been removed forms the conical connection portion 16. The connection portion 16 is formed as a cone shape by an etching factor. The second copper layer 12 is not etched by an etching resist layer 13 and the upper resist layer 14.
As shown in FIGS. 2D and 2E, the resist layer 14 of FIG. 2C is removed, then a prepreg film 17 is attached to the end of each connection portion 16, and then the prepreg film 17 is pressurized by a roller (not shown) thereby to position between each connection portion 16.
As shown in FIG. 2F, a third copper layer 18 is connected to the end of the prepreg film 17 and the connection portion 16 by a pressing.
As shown in FIG. 2G, copper patterns 19 are respectively formed at the upper and lower surfaces of the base member 10. According to this, the copper patterns 19 are electrically connected one another by the connection portion 16.
However, the conventional fabricating method for a printed circuit board has the following problems.
First, the conventional fabricating method for a printed circuit board using an anisotropy conductive adhesive is not suitable for a printed circuit board requiring a low resistance.
Second, in the conventional fabricating method for a printed circuit board, a hole has to be formed by a perforation at the printed circuit board and a plating has to be performed at the inner circumferential surface of the hole thereby to have very complicated processes.
Third, according to the conventional fabricating method for a printed circuit board disclosed in the Korean Patent No. 203, 540, a conductive wiring part (a connection portion) has to be formed with a certain height by repeatedly printing a conductive paste several times, and the conductive wiring part has to be formed at a precise position thereby to have a complicated entire process and thus to lower a production yield. Since a diameter of a lower portion of the conductive wiring part is relatively larger than a diameter of an upper portion thereof, a gap between the conductive wiring parts becomes increased and thereby the printed circuit board can not be minimized.
Fourth, according to the conventional printed circuit board disclosed in the Japanese Laid-Open Publication Patent No. 2001-11189, the first copper layer 11 has to be relatively thicker in order to form the connection portion 16 with a certain height, and many parts of the first copper layer 11 are unnecessarily consumed in order to form the connection portion 16. At the time of etching the connection portion 16, a diameter of the end of the connection portion 16 becomes smaller than a diameter of a bottom portion thereof. Therefore, a gap between adjacent connection portions 16 has to be properly obtained in order to constantly form the diameter of the end of the connection portion 16, thereby having a difficulty in forming a minute circuit pattern.
Also, a thickness of the second copper 12 is less than 20 μm and a thickness of the first copper layer 11 for forming the connection portion 16 is approximately 100 μm, so that the second copper layer 12 is bent at the time of dealing with the base member 10 after forming the connection portion 16.
Also, if a height of the connection portion 16 finally required is 60 μm, for example, a thickness of the first copper layer 11 has to be more than approximately 100 μm with consideration of a loss due to an etching, a loss due to a pressurization, etc. According to this, a material loss is entirely increased.